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Notes for 3.13
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Objectives
Discuss why Mendel’s principles cannot be applied to all situations.
Compare and contrast different types of complex inheritance.
It’s complicated
Mendel got lucky
All of the traits that he studied were only controlled by two alleles
Remember: an allele is a form of one gene (yellow or green)
All of the traits were perfectly dominant or recessive
It’s complicated
Unfortunately, most traits are not so neat and tidy
It’s complicated
There are 4 forms of complex inheritance you need to know
Incomplete dominance
Co-dominance
Multiple Alleles
Polygenic inheritance
Incomplete Dominance
Remember, a gene is the instruction for a protein
Because there are two alleles for a trait, two proteins are being produced
In Mendel’s studies, one protein dominated the other
The dominant protein was shown
Incomplete Dominance
Incomplete Dominance: One gene does not clearly dominate the other
The phenotype of the offspring is a blend of the two parent phenotypes
Incomplete Dominance
Example: A white flower is mixed with a red flower
In incomplete dominance a white flower mixed with a red flower produces PINK offspring
The offspring are a blend of the two parents
Neither parent is seen in the offspring
Co-dominance
Co-dominance: Neither phenotype dominates and BOTH are shown
Co-dominance
Example: A red flower is mixed with a white flower
In co-dominance a red parent flower and a white parent flower produce offspring with BOTH red AND white petals
Compare
Incomplete dominance:
Red + White = Pink
Co-dominance:
Red + White = Both red and white on the same flower
Multiple Alleles
With all of the variety in the world it would make sense that some traits have more than two forms
Multiple Alleles
Multiple Alleles: A trait for which there are more than 2 forms of a gene
Multiple Alleles
Example: Blood Type
There are three alleles for blood type
IA
IB
i
Multiple Alleles
Genotypes for type A blood are
IA IA or IAi
Genotypes for type B blood are
IB IB or IBi
Genotype for AB blood is
IA IB
Genotype for type O blood is
ii
Polygenic Inheritance
If you have noticed, most kids are a blend of their parents traits
To this point all of the traits we have talked about have been controlled by different forms of ONE gene
Polygenic Inheritance
Polygenic Inheritence
Remember your words
Poly = many
What do you think POLYgenic inheritance means?
Polygenic Inheritance
Polygenic inheritance: A trait that is controlled by multiple genes working together
Some good examples
Skin color
Eye color
Height
Polygenic Inheritance
There are many genes that control skin color, eye color, or height
The interaction of those genes controls the precise color of your skin, color of your eyes, or your height